The Pro Trucker PTRV1-HDM is a 3-Way mirror mount for CB radio antennas. Featuring a heavy-duty beehive SO-239 stud, the PTRV1-HDM is great for mounting all types of antennas with a standard 3/8" x 24 thread. Flexible to use, the groove can be set horizontally or vertically. Pro Trucker mounts are easy to install, and guaranteed to last!